Exemplary embodiments of the present invention relate to a 3rd generation partnership project (3GPP) long term evolution (LTE) system, and more particularly, to a method for deciding an unregistered macrocell user equipment (MUE) adjacent to a femtocell base station, which decides an MUE influenced by interference around a femtocell base station using a handover defined in the 3GPP LTE standard.
In the 3GPP LTE, the standardization on a femtocell base station is conducted to remove a shadow area of a user equipment indoors and secure a high-speed data transmission rate.
The femtocell base station (home evolved node B; HeNB) is a femto-sized base station using low power, and provides a radio access service coverage narrower than a macrocell base station. Since the HeNB uses the same radio interface as the macrocell base station, the HeNB can provide a service without adding a separate interface to a radio user equipment. Further, since the HeNB is connected to a core network by accessing a public network through Ethernet and a cable modem, the HeNB has low installation and management cost as compared with the macrocell base station using a provider private network.
The macrocell base station (macro evolved node B; MeNB) uses an open access for providing a downlink radio access service to all user equipments (UEs) existing in its own service coverage.
On the other hand, the MeNB basically uses a closed subscriber group (CSG) for providing a radio access service to only a previously registered UE. In order to support the CSG, each HeNB receives a unique CSG identity (CSG ID) provided in the same public land mobile network (PLMN), and each UE has a CSG list (CSG whitelist) in which the unique CSG ID of a HeNB having a service coverage is stored.
In order for a macrocell UE (MUE) to receive the downlink radio access service from a HeNB, an identification number of the corresponding HeNB is necessarily included in an identification number list of the MUE.
If the MUE approaches a HeNB of which identification number is not registered in its identification number list, the MUE cannot receive a radio access service in the corresponding HeNB.
Therefore, if the corresponding HeNB is in course of providing a radio access service to a femtocell UE (home UE: HUE) through the same channel in terms of the downlink, the signal-to-interference noise ratio (SINR) performance of the MUE is considerably lowered due to an interference caused by a leakage signal of the HeNB, and therefore, deterioration of call quality or call-drop may occur.
Accordingly, when an MUE is influenced by interference of a HeNB while remaining in an existing cell due to an access limitation to the HeNB in which the MUE is not registered, there is provided a method for reducing the interference.
The background art of the present invention has been disclosed in Korean Patent Laid-Open Publication No. 10-2011-0067604, filed on Jun. 22, 2011.